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Sunday, May 27, 2012

Strong Thunderstorm Hits Portland

For the second day in a row, convection and thunderstorms developed over the Cascades and rolled into the western lowlands...in this case hitting southwest Washington, Portland, and the northern Willamette Valley. Mark Albright, past WA state climatologist, reported that an observer in downtown Vancouver just W of I-5 reported 0.40 inches of rain in 5-minutes from 19:29 to 19:34 PDT 26 May 2012. The highest hourly amount from the Portland Hydra network (46 sites) seemed to be the 1.34 inches over one hour from 19:00 to 20:00 PDT reported at Hayden Island just west of I-5. This is extraordinarily heavy precipitation--heavier that the downpour that hit Seattle in December 14, 2005.....the event that flooded parts of the Madison valley. Most gutters simply can't handle this intensity.

Take a look at the Portland radar at 7:26 PM Saturday....see those reds?...that is torrential rain.

Here is the storm total precipitation from the radar...you can see the track of the heavier rainfall.

Did the models get it right?....unfortunately, not....again they failed. As proof, take a look at the forecast 24 h precp ending 5 AM Sunday....not good. This summer I plan on examining this event in detail....hopefully finding the origin of this failure. But convection is hard to forecast, particularly weakly forecast convection.

6 comments:

Yup. It was weird because Vancouver rarely gets whopper T-storms. At my house- lots of rain, very little hail. At my friend's house 1/2 a mile away, tons of rain and dime sized hail piled up in drifts.It didn't last as long as Friday night's T-storm, and I don't think any trees got hit like in Friday's storm.All in all, a really fun weather weekend for us!

In terms of thunder and lightning, Friday's storm over Portland was much more impressive. However, Saturday's storm definitely brought the rain as you mentioned. My own sensor reported .71 inches in 24 hrs. I haven't looked at the hourly data yet, but since it had been dry the rest of the day, that should have all come from the thunderstorm.

I'll have to say that, subjectively speaking, Saturday's storm was the most intense downpour I have ever experienced! I was on my bike in NE Portland and was lucky enough to be able to take shelter under a shelter in Irving Park. When it finally left and I headed out again I discovered the nearby streets to be under a foot and more of water. This on a day with a forecast of "10 percent chance of showers." I'm glad to know that the world can still manage to elude prediction though. Y'know?

It was crazy out in Hillsboro too. The airport ASOS just 1 mile to my North had only 0.23 inches in that hour but several personal weather stations. Here is the video from my location: http://www.youtube.com/watch?v=1bX5fgVKYsU

Also, just one mile to my South. They received well over 1" in just 30 minutes according to Weather Underground PWS's